Priority is claimed with respect to Application No. 100 04 714.9-24 filed in Germany on Feb. 3, 2000, the disclosure of which is incorporated herein by reference.
The invention relates to an apparatus for casting a molded part, the apparatus including a casting mold having a lower core, an upper core and pushing elements which, in a first end position, are in contact so as to form a hollow space into which a liquid casting mass can be introduced, with the upper core, which rests against the inside of the molded part, being displaced in an insertion direction in order to remove the molded part comprising a hardened casting mass.
An apparatus of this type is particularly useful for casting aluminum molded parts, such as automobile wheel rims.
To form the casting mold, the upper core is moved from above toward the lower core in the insertion direction. The pushing elements move laterally toward the upper and lower cores, so as to form the hollow space between the pushing elements, the upper core and the lower core, into which the liquid casting mass, preferably liquid aluminum, is poured.
The molded part corresponding to the shape of the hollow space has side walls that are essentially located between the pushing elements and the upper core, and a front wall that is located between the upper and lower cores, and is open to the rear side.
After the casting mass has hardened into the molded part, the upper core is moved upward again in the insertion direction, and removed from the molded part by way of the rear opening of the part. The molded part can be detached from the lower core and removed after the pushing elements have been removed.
As the upper core is removed from the molded part, the outside wall of the upper core slides along the inside of the molded part.
To make the upper core detachable from the molded part, the inside diameter of the molded part tapers continuously toward the front wall. Accordingly, the outside diameter of the upper core tapers continuously toward the front end.
If, in contrast, the upper core were to have a local widened area of its cross section that protruded beyond a jacket surface of the upper core, the inside of the side wall of the molded part would have a corresponding recess that would surround the widened cross section. Thus, the upper core would be fixedly held against the molded part, and could not be detached from the molded part.
It is, however, often desirable to create such recesses or, in general, undercut regions on the inside of the molded part. Undercut regions of this type may be required due to the desired shape of the molded part, for example to assure specific functions of the molded part. In addition, such undercut regions can also contribute to considerable material savings. Cutting these regions into the molded parts would necessitate additional processing after the casting procedure.
These additional manufacturing steps require an undesired additional outlay for machinery and labor, which significantly increases the production costs for these molded parts.
It is an object of the invention to embody an apparatus of the type mentioned at the outset such that undercut regions can be created in the respective molded part during the casting process.
The above and other objects are accomplished according to the invention by the provision of a casting mold having a lower core, an upper core and pushing elements which are movable into a position in contact with one another to form a hollow space into which a liquid casting mass can be introduced during a casting process, with the upper core, which rests against the inside of the molded part, being displaceable in an insertion direction in order to remove the molded part constituted by a hardened casting mass, the upper core having a jacket surface and a bore that extends at a predetermined angle with respect to the insertion direction; an actuating element displaceable in the insertion direction; a crossbeam; and an undercut pushing element coupled to the actuating element via the crossbeam and having a front end that is movable between first and second end positions, wherein due to a displacement of the actuating element, the undercut pushing element travels in the bore of the upper core with the front end of the undercut pushing element protruding laterally beyond the jacket surface of the upper core in the first end position during the casting process, and with the front end of the undercut pushing element assuming the second end position that is one of (a) flush with the jacket surface of the upper core and (b) disposed behind the jacket surface, when the upper core is removed from the casting mold.
The apparatus according to the invention thus has an actuating element that can be displaced in the insertion direction, and to which an undercut pushing element is coupled, via a crossbeam, such that the undercut pushing element travels in a bore in the upper core, which extends at a predetermined angle with respect to the insertion direction, when the actuating element is actuated.
During the casting process, the undercut pushing element assumes a first end position, in which its front end protrudes laterally beyond the jacket surface of the upper core. When the upper core is removed, the front end of the undercut pushing element assumes a second end position which ends flush with the jacket surface of the upper core, or lies behind the jacket surface.
The undercut pushing element of the invention can be used to create defined undercut regions at predetermined locations on the inside of the molded part. The size and shape of the undercut regions can be predetermined simply through the selection of the front end of the undercut pushing element. It is especially advantageous to provide a plurality of undercut pushing elements for creating numerous undercut regions.
An essential advantage of the apparatus of the invention is that the undercut regions can be cut into the molded part during the casting process without impeding the removal of the upper core from the inside region of the molded part.
For this purpose, prior to the casting process, the actuating element displaces the undercut pushing element into its first end position, in which the front end of the undercut pushing element protrudes beyond the jacket surface of the upper core. Accordingly, a corresponding undercut region is created on the inside of the molded part during the casting process.
After the casting mass has hardened into the molded part, the actuating element displaces the undercut pushing element into its second end position, so the front end of the undercut pushing element no longer protrudes beyond the jacket surface of the upper core. Thus, the upper core can be removed from the molded part unimpeded.
A further significant advantage of the invention is that the undercut pushing element is coupled to the actuating element via the crossbeam. The crossbeam converts the linear movement of the actuating element into a likewise linear movement of the undercut pushing element, so the undercut pushing element does not execute a movement parallel to the insertion direction, in which the actuating element moves, but at a predetermined angle with respect to this direction. The angle is determined by the embodiment of the crossbeam, and is preferably between 90xc2x0 and 180xc2x0.
It is particularly advantageous that an actuating element that moves parallel to the insertion direction can move the undercut pushing element.
The actuating element can be simply coupled to the moving mechanisms for moving the upper core, which is likewise moved in the insertion direction.
The moving mechanism for deflecting the undercut pushing element can therefore be produced with low labor and cost requirements.
In an especially advantageous embodiment, the apparatus of the invention is used to produce automobile wheel rims, preferably comprising aluminum.
In this case, the undercut regions are preferably disposed where the spokes are connected to the rim base of the automobile wheel rim.
The undercut regions considerably reduce the weight of such automobile wheel rims, for example by 400 g to 1000 g, depending on the rim embodiment. This results in significant material and cost savings.
A further advantage is that the undercut regions prevent the formation of undesired material buildup, and therefore bubbles, which greatly reduces the rejection quotas in the production of automobile wheel rims.
The creation of undercut regions lends the automobile wheel rim an essentially constant wall thickness, resulting in better casting and an improved distribution of force over the automobile wheel rim, which greatly increases the stability of the automobile wheel rim.